Field of the Invention
The present invention relates to a watermark embedding apparatus and a watermark embedding method, and more particularly, to a watermark embedding apparatus and a watermark embedding method for efficiently enhancing robustness of watermark insertion.
Discussion of the Related Art
Digital watermarking is a technique used for protecting copyrights and determining forgery of digital contents by embedding non-cognitive unique information in various literary productions including an audio, an image, a moving picture, and the like and enabling tracking the literary productions through extraction of the embedded information afterwards. In particular, a trend that illegal outflow and distribution of moving picture contents such as a movie or a TV broadcast rapidly increase is shown, and as a result, as a countermeasure against, a watermark technique is emerging.
FIG. 1A is a basic conceptual view of watermark embedding.
Referring to FIG. 1A, the watermark embedding apparatus generates a watermarked image I′ by embedding a watermark pattern in an image I input within a range in which an original is audiovisually similarly viewed by configuring a watermark pattern W. In this case, watermark information is modulated by using a secret/public key K to generate a watermark pattern having the same size as an original image. The secret key is used for a purpose of preventing the watermark information from being interpreted by an authorized user and preventing the watermark and another watermark from interfering with each other by allowing the watermark patterns of both watermarks to be orthogonal to each other when another watermark is inserted into contents in which the watermark is already embedded by using the same watermark technique.
FIG. 1B is a basic conceptual view of watermark detection.
Referring to FIG. 1B, a watermark detecting apparatus may detect a watermark through the secret/public key K by receiving a test image I′. In this case, it is determined whether the detected watermark is the same as the watermark W originally embedded by the embedding apparatus to determine whether to attack the corresponding image.
The contents in which the watermark is embedded are intentionally or unintentionally attacked under various environments and need to have robustness to survive even after being attacked. In the case of the moving picture contents, the moving picture contents are subjected to a compression operation several times until the moving picture contents are transferred from a content provider to the user and each step is performed through lossy compression, and as a result, an embedded watermark signal cannot be avoided. Moreover, in recent years, with the development of compression technology, as compression efficiency has further increased, a risk of the watermark signal embedded in a low-frequency band has been further increased in a compression step in order to secure invisibility.
The compression is naturally performed in a transmission step, while a compression attack having a malicious purpose is even stronger in compression strength, and as a result, a countermeasure associated with moving picture compression for securing the robustness of the watermark is required.
As moving picture encoding, a method is primarily used, which decides a key frame through conditions including a scenecut among several consecutive frames, and the like and thereafter, encodes only a difference value from similar frames. In this case, the key frame is subjected to lossless compression and since other frames which refer to the key frame may not have a lot of information, compression of other frames becomes the lossy compression. When the watermark signal is to be embedded in the frame in which the lossy compression is performed, almost most signals disappear, and as a result, it is difficult to detect the watermark.